Disclosed is a high-energy lithium secondary battery including: a cathode including, as cathode active materials, a first cathode active material represented by Formula 1 below and having a layered structure and a second cathode active material represented by Formula 2 below and having a spinel structure, wherein the amount of the first cathode active material is between 40 and 100 wt % based on a total weight of the cathode active materials; an anode including amorphous carbon having a capacity of 300 mah/g or more; and a separator.
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1. A high-energy lithium secondary battery comprising:
a cathode comprising, as cathode active materials, a first cathode active material represented by Formula (1)
Lix(NivMnwCoyMz)O2-tAt (1) wherein 0.8<x≦1.3, 0≦v≦0.9, 0≦w≦0.9, 0≦y≦0.9, 0≦z≦0.9, x+v+w+y+z=2, and 0≦t≦0.2; M denotes at least one metal or transition metal cation having an oxidation number of +2 to +4;
and A is a monovalent or divalent anion,
and having a layered structure; and
a second cathode active material represented by Formula (2)
LiaMn2-bM′bO4-cA′c (2) wherein 0.8<a≦1.3, 0≦b≦0.5, and 0≦c≦0.3; M′ denotes at least one metal or transition metal cation having an oxidation number of +2 to +4; and A′ is a monovalent or divalent anion,
and having a spinel structure,
wherein an amount of the first cathode active material is between 40 and 100 wt % based on a total weight of the first and second cathode active materials;
an anode comprising amorphous carbon having a capacity of 300 mah/g or more, wherein the amorphous carbon is a mixture of a first carbon having a specific surface area with respect to capacity of 0.01 to 0.031 m2/mah and a second carbon having a specific surface area with respect to capacity of 0.0035 to 0.017 m2/mah, wherein the first carbon has a powder conductivity of 15 S/cm to less than 100 S/cm at a powder density of 1.0 to 1.2 g/cc, and wherein the second carbon has a powder conductivity of 30 S/cm to less than 100 S/cm at a powder density of 1.4 to 1.6 g/cc;
and a separator.
2. The high-energy lithium secondary battery according to
3. The high-energy lithium secondary battery according to
4. The high-energy lithium secondary battery according to
5. The high-energy lithium secondary battery according to
6. The high-energy lithium secondary battery according to
7. The high-energy lithium secondary battery according to
8. The high-energy lithium secondary battery according to
9. The high-energy lithium secondary battery according to
10. A battery module comprising the lithium secondary battery according to
11. An electric vehicle or hybrid electric vehicle comprising the battery module according to
12. A power storage device comprising the battery module according to
13. The high-energy lithium secondary battery according to
14. The high-energy lithium secondary battery according to
15. The high-energy lithium secondary battery according to
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The present application is a continuation of International Application No. PCT/KR2012/005473 filed on Jul. 11, 2012, which claims the benefit of Korean Patent Application No. 10-2011-0069539 filed on Jul. 13, 2011, the disclosures of which are incorporated herein by reference.
The present invention relates to a high-energy lithium secondary battery having enhanced energy density characteristics. More specifically, the present invention relates to a high-energy lithium secondary battery including: a cathode including, as cathode active materials, a first cathode active material represented by Formula 1 below and having a layered structure and a second cathode active material represented by Formula 2 below and having a spinel structure, wherein the amount of the first cathode active material is between 40 and 100 wt % based on a total weight of the cathode active materials; an anode including amorphous carbon having a capacity of 300 mAh/g or more; and a separator.
As mobile device technology continues to develop and demand therefor continues to increase, demand for secondary batteries as energy sources is rapidly increasing. In addition, secondary batteries have recently been used as power sources for electric vehicles (EVs), hybrid electric vehicles (HEVs), and the like. Accordingly, research into secondary batteries that can meet a variety of demands is underway and, in particular, demand for lithium secondary batteries having high energy density, high discharge voltage and high output stability is increasing.
Conventionally, a lithium cobalt composite oxide having a layered structure is generally used as a cathode active material of a lithium secondary battery. When such lithium cobalt composite oxide is used as a cathode active material, however, cobalt as a main component is very expensive, and the layered structure thereof undergoes changes in volume according to repeated intercalation and deintercalation of Li ions and collapses when more than half of the Li ions are deintercalated. Thus, lithium secondary batteries including such cathode active materials are not suitable for use in EVs or large capacity power storage devices in terms of safety.
In addition, a battery including a lithium manganese composite oxide having a spinel structure is not suitable for use as an energy source for EVs requiring relatively high energy density since a travel distance thereof is determined by battery electric energy.
Meanwhile, crystalline graphite is mainly used as an anode active material, which has a very low discharge potential of about −3 V with respect to a standard hydrogen electrode potential, and exhibits very reversible charge/discharge behavior due to uniaxial orientation of a graphene layer and thus has excellent cycle lifespan.
Examples of carbonaceous active materials include crystalline graphite and amorphous carbon. Among these, amorphous carbon has excellent output characteristics while having low energy density (i.e., less than 300 mAh/g) and thus batteries including such amorphous carbon are not suitable for use as an energy source for EVs.
The present invention aims to address the aforementioned problems of the related art and to achieve technical goals that have long been sought.
Thus, an object of the present invention is to provide a lithium secondary battery that exhibits the same output level as that of a lithium secondary battery using conventional amorphous carbon and enhanced energy density.
In accordance with one aspect of the present invention, provided is a high-energy lithium secondary battery including: a cathode including, as cathode active materials, a first cathode active material represented by Formula 1 below and having a layered structure and a second cathode active material represented by Formula 2 below and having a spinel structure, wherein the amount of the first cathode active material is between 40 and 100 wt % based on a total weight of the cathode active materials; an anode including amorphous carbon having a capacity of 300 mAh/g or more; and a separator.
Lix(NivMnwCoyMz)O2-tAt (1)
In Formula 1,
0.8<x≦1.3, 0≦v≦0.9, 0≦w≦0.9, 0≦y≦0.9, 0≦z≦0.9, x+v+w+y+z=2, and 0≦t≦0.2;
M denotes at least one metal or transition metal cation having an oxidation number of +2 to +4; and A is a monovalent or divalent anion.
LiaMn2-bM′bO4-cA′c (2)
In Formula 2, 0.8<a≦1.3, 0≦b≦0.5, and 0≦c≦0.3; M′ denotes at least one metal or transition metal cation having an oxidation number of +2 to +4; and A′ is a monovalent or divalent anion.
The amorphous carbon may be one selected from the group consisting of a first carbon having a specific surface area (with respect to capacity) of 0.01 to 0.031 and a second carbon having a specific surface area (with respect to capacity) of 0.0035 to 0.0170 or a mixture thereof. When the first carbon and the second carbon are used in combination, a weight ratio of the first carbon to the second carbon may be in the range of 1:9 to 9:1.
In particular, the first carbon has a powder conductivity of 15 S/cm to less than 100 S/cm at a powder density of 1.0 to 1.2 g/cc, and the second carbon has a powder conductivity of 30 S/cm to less than 100 S/cm at a powder density of 1.4 to 1.6 g/cc.
The amounts of the first cathode active material having a layered structure of Formula 1 and the second cathode active material having a spinel structure of Formula 2 may be in the range of 50 wt % to 90 wt % and in the range of 10 wt % to 50 wt %, respectively, based on the total weight of the first and second cathode active materials.
In a specific embodiment of the present invention, the first cathode active material may be a layered crystalline structure lithium transition metal oxide having an average particle diameter (with respect to capacity) of 0.03 to 0.1 μm/mAh and a powder conductivity of 1×10−3 S/cm to less than 10×10−3 S/cm at a powder density of 2.65 to 2.85 g/cc.
In a particular embodiment, the first cathode active material of Formula 1 may be a layered crystalline structure lithium transition metal oxide satisfying conditions that the oxide includes mixed transition metals of Ni and Mn, an average oxidation number of the total transition metals excluding lithium exceeds +3, and the amount of Ni is the same or greater than that of Mn on a molar ratio basis.
In addition, in another particular embodiment, the lithium transition metal oxide of Formula 1 may be Li(Ni0.5Mn0.3Co0.2)O2 or Li(Ni1/3Mn1/3Co1/3)O2.
In Formula 1, the transition metal such as Ni, Mn, or Co may be substituted with a metal and/or other transition metal (M) elements having an oxidation number of +2 to +4. In particular, the transition metal may be substituted with at least one selected from the group consisting of Al, Mg, and Ti. In this case, a substitution amount may satisfy the condition: 0.3≦z≦0.6.
In addition, in a specific embodiment of the present invention, the second cathode active material may be a spinel crystalline structure lithium transition metal oxide having an average particle diameter (with respect to capacity) of 0.1 to 0.2 μm/mAh and a powder conductivity of 1×10−5 S/cm to less than 10×10−5 S/cm at a powder density of 2.65 to 2.85 g/cc.
In Formula 2, M′ may be at least one selected from the group consisting of Co, Mn, Ni, Al, Mg, and Ti.
In addition, in Formulas 1 and 2, the oxygen ion may be substituted with a monovalent or divalent anion (A, A′) within a predetermined range, wherein A and A′ may each independently be at least one selected from the group consisting of halogens such as F, Cl, Br, and I, S, and N.
Substitution of these anions enables high binding ability with the transition metals and prevention of structural transition of the compound, whereby the lithium secondary battery may have improved lifespan. On the other hand, when the substitution amounts of A and A′ are too high (t>0.2), the lifespan of the lithium secondary battery may rather be deteriorated due to incomplete crystal structure.
In the cathode active material of Formula 1 or 2, when O is substituted with a halogen or the transition metal such as Ni, Mn, or the like is substituted with another transition metal (M, M′), the corresponding compound may be added prior to high-temperature reaction.
According to experimental results confirmed by the inventors of the present invention, the lithium secondary battery according to the present invention exhibits high energy density characteristics within the above-described ranges of amounts and physical quantities. The physical quantities may be measured using measurement methods known in the art. In particular, the specific surface area may be measured by BET, the powder density may be measured using a true density measurement method, and the powder conductivity may be measured by measuring sheet resistance after forming a powder into a pellet.
The high-energy lithium secondary battery including the cathode and anode active materials having the aforementioned particular physical quantities has a capacity with respect to volume of 0.05 to 0.09 Ah/cm3 and an energy with respect to volume of 0.2 to 0.4 Wh/cm3.
The separator is disposed between the cathode and the anode and, as the separator, a thin insulating film with high ion permeability and high mechanical strength is used. The separator generally has a pore diameter of 0.01 to 10 μm and a thickness of 5 to 300 μm.
As the separator, sheets or non-woven fabrics, made of an olefin polymer such as polypropylene; or glass fibers or polyethylene, which have chemical resistance and hydrophobicity, or kraft papers are used. Examples of commercially available separators include Celgard series such as Celgard® 2400 and 2300 (available from Hoechest Celanese Corp.), polypropylene separators (available from Ube Industries Ltd., or Pall RAI Co.) and polyethylene series (available from Tonen or Entek).
In a specific embodiment of the present invention, the separator may be a polyolefin-based separator and an organic-inorganic composite separator including an inorganic material such as silicon. Prior patent applications of the present applicant disclose the fact that the organic-inorganic composite separator enables improved safety or the like of lithium secondary batteries.
The present invention also provides a medium to large-scale battery module including the above-described high energy density lithium secondary battery as a unit battery and a medium to large-scale battery pack including the battery module.
In addition, the present invention provides a device using the battery pack as a power source. In particular, the battery pack may be used as a power source of electric vehicles, hybrid electric vehicles, plug-in hybrid vehicles, or power storage devices.
The configuration of the medium to large-scale battery module and battery pack and fabrication thereof are known in the art, and thus, a detailed description thereof will be omitted herein.
The cathode may be manufactured by coating, on a cathode current collector, a slurry prepared by mixing a cathode mixture including the cathode active material with a solvent such as NMP or the like and drying and rolling the coated cathode current collector.
The cathode mixture may optionally include a conductive material, a binder, a filler, or the like, in addition to the cathode active material.
The cathode current collector is generally fabricated to a thickness of 3 to 500 μm. The cathode current collector is not particularly limited so long as it does not cause chemical changes in the fabricated lithium secondary battery and has high conductivity. For example, the cathode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, silver, or the like, an aluminum-cadmium alloy, or the like. The cathode current collector may have fine irregularities at a surface thereof to increase adhesion between the cathode active material and the cathode current collector. In addition, the cathode current collector may be used in any of various forms including films, sheets, foils, nets, porous structures, foams, and non-woven fabrics.
The conductive material is typically added in an amount of 1 to 30 wt % based on the total weight of the mixture including the cathode active material. There is no particular limit as to the conductive material, so long as it does not cause chemical changes in the fabricated battery and has conductivity. Examples of conductive materials include graphite such as natural or artificial graphite; carbon black such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black; conductive fibers such as carbon fibers and metallic fibers; metallic powders such as carbon fluoride powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; conductive metal oxides such as titanium oxide; and polyphenylene derivatives.
The binder is a component assisting in binding between the active material and the conductive material and in binding of the active material to the cathode current collector. The binder is typically added in an amount of 1 to 30 wt % based on the total weight of the mixture including the cathode active material. Examples of the binder include, but are not limited to, polyvinylidene fluoride, polyvinyl alcohols, carboxymethylcellulose (CMC), starch, hydroxypropylcellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluorine rubber, and various copolymers.
The filler is optionally used as a component to inhibit cathode expansion. The filler is not particularly limited so long as it is a fibrous material that does not cause chemical changes in the fabricated battery. Examples of the filler include olefin-based polymers such as polyethylene and polypropylene; and fibrous materials such as glass fiber and carbon fiber.
As a dispersion solution, isopropyl alcohol, N-methylpyrrolidone (NMP), acetone, or the like may be used.
Uniform coating of an electrode material paste on a metallic material may be performed using a method selected from among known methods or a new appropriate method in consideration of properties of the electrode material. For example, the coating process may be performed by applying the paste to the cathode current collector and uniformly dispersing the paste thereon using a doctor blade. In some embodiments, the application and dispersion processes may be implemented as a single process. The coating process may be performed by, for example, die-casting, comma coating, screen-printing, or the like. In another embodiment, the paste may be molded on a separate substrate and then adhered to a current collector via pressing or lamination.
The drying of the coated paste on a metallic plate may be performed in a vacuum oven at a temperature between 50 and 200° C. for a period of one day.
The anode may be manufactured by coating the anode active material on an anode current collector and drying the coated anode current collector. As desired, components such as the above-described conductive material, binder and filler may further be optionally added to the anode active material.
The anode current collector is typically fabricated to a thickness of 3 to 500 μm. The anode current collector is not particularly limited so long as it does not cause chemical changes in the fabricated secondary battery and has conductivity. For example, the anode current collector may be made of copper, stainless steel, aluminum, nickel, titanium, sintered carbon, copper or stainless steel surface-treated with carbon, nickel, titanium, or silver, aluminum-cadmium alloys, or the like. As in the cathode current collector, the anode current collector may also have fine irregularities at a surface thereof to enhance adhesion between the anode current collector and the anode active material. In addition, the anode current collector may be used in various forms including films, sheets, foils, nets, porous structures, foams, and non-woven fabrics.
A lithium salt-containing non-aqueous electrolyte is composed of a non-aqueous electrolyte and a lithium salt. As the non-aqueous electrolyte, a non-aqueous electrolytic solution, an organic solid electrolyte, or an inorganic solid electrolyte may be used.
For example, the non-aqueous electrolytic solution may be an aprotic organic solvent such as N-methyl-2-pyrrolidinone, propylene carbonate, ethylene carbonate, butylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, gamma butyrolactone, 1,2-dimethoxy ethane, 1,2-diethoxy ethane, tetrahydrofuran, 2-methyl tetrahydrofuran, dimethylsulfoxide, 1,3-dioxolane, 4-methyl-1,3-dioxene, diethylether, formamide, dimethylformamide, dioxolane, acetonitrile, nitromethane, methyl formate, methyl acetate, phosphoric acid triester, trimethoxy methane, dioxolane derivatives, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, propylene carbonate derivatives, tetrahydrofuran derivatives, ether, methyl propionate, or ethyl propionate.
Examples of the organic solid electrolyte include polyethylene derivatives, polyethylene oxide derivatives, polypropylene oxide derivatives, phosphoric acid ester polymers, poly agitation lysine, polyester sulfide, polyvinyl alcohols, polyvinylidene fluoride, and polymers containing ionic dissociation groups.
Examples of the inorganic solid electrolyte include nitrides, halides and sulfates of lithium (Li) such as Li3N, LiI, Li5NI2, Li3N—LiI—LiOH, LiSiO4, LiSiO4—LiI—LiOH, Li2SiS3, Li4SiO4, Li4SiO4—LiI—LiOH, and Li3PO4—Li2S—SiS2.
The lithium salt is a material that is readily soluble in the non-aqueous electrolyte and examples thereof include LiCl, LiBr, LiI, LiClO4, LiBF4, LIB10Cl10, LiPF6, LiCF3SO3, LiCF3CO2, LiAsF6, LiSbF6, LiAlCl4, CH3SO3Li, CF3SO3Li, LiSCN, LiC(CF3SO2)3, (CF3SO2)2NLi, chloroborane lithium, lower aliphatic carboxylic acid lithium, lithium tetraphenyl borate, and imide.
In addition, in order to improve charge/discharge characteristics and flame retardancy, for example, pyridine, triethylphosphite, triethanolamine, cyclic ether, ethylenediamine, n-glyme, hexaphosphoric triamide, nitrobenzene derivatives, sulfur, quinone imine dyes, N-substituted oxazolidinone, N,N-substituted imidazolidine, ethylene glycol dialkyl ether, ammonium salts, pyrrole, 2-methoxy ethanol, aluminum trichloride, or the like may be added to the electrolyte. In some cases, in order to impart incombustibility, the electrolyte may further include a halogen-containing solvent such as carbon tetrachloride and ethylene trifluoride. In addition, in order to improve high-temperature storage characteristics, the electrolyte may further include carbon dioxide gas, fluoro-ethylene carbonate (FEC), propene sultone (PRS), fluoro-propylene carbonate (FPC), or the like.
Now, the present invention will be described in more detail with reference to the following examples. These examples are provided only for illustration of the present invention and should not be construed as limiting the scope and spirit of the present invention.
A cathode active material prepared by mixing LiNi1/3CO1/3Mn1/3O2 having an average particle diameter (with respect to capacity) of 0.05 μm/mAh and LiMn2O4 having an average particle diameter (with respect to capacity) of 0.14 μm/mAh in a mixing ratio of 70:30, a conductive material, and a binder were prepared in a weight ratio of 89:6.0:5.0 and then were added to NMP and mixed therein to prepare a cathode mixture. Subsequently, the cathode mixture was coated on an Al foil having a thickness of 20 μm and rolled and dried, thereby completing fabrication of a cathode.
Similarly, an anode active material prepared by mixing a first carbon having a specific surface area (with respect to capacity) of 0.020 m2/mAh and a second carbon having a specific surface area (with respect to capacity) of 0.012 m2/mAh in a mixing ratio of 30:70, a conductive material, and a binder were prepared in a weight ratio of 96:1.5:2.5, added to a mixer, and mixed therein to prepare an anode mixture. Subsequently, the anode mixture was coated on a Cu foil having a thickness of 10 μm and rolled and dried, thereby completing fabrication of an anode.
In this regard, LiNi1/3Co1/3Mn1/3O2 had a powder conductivity of 1.0×10−3 S/cm at a powder density of 2.75 g/cc, LiMn2O4 had a powder conductivity of 5×10−5 S/cm at a powder density of 2.80 g/cc, the first carbon had a powder conductivity of 30 S/cm at a powder density of 1.1 g/cc, and the second carbon had a powder conductivity of 65 S/cm at a powder density of 1.5 g/cc. The cathode, the anode, and a carbonate electrolytic solution containing 1M LiPF6 as an electrolyte were used to manufacture a battery.
A battery was manufactured in the same manner as in Example 1, except that the mixing ratio of LiNi1/3Co1/3Mn1/3O2 to LiMn2O4 in the cathode active material was 80:20.
A battery was manufactured in the same manner as in Example 1, except that a second carbon was used instead of the first carbon.
A battery was manufactured in the same manner as in Example 3, except that the mixing ratio of LiNi1/3Co1/3Mn1/3O2 to LiMn2O4 in the cathode active material was 80:20.
A battery was manufactured in the same manner as in Example 1, except that an anode active material prepared by mixing the first carbon and the second carbon in a mixing ratio of 70:30 was used.
A battery was manufactured in the same manner as in Example 5, except that the mixing ratio of LiNi1/3Co1/3Mn1/3O2 to LiMn2O4 in the cathode active material was 80:20.
A battery was manufactured in the same manner as in Example 1, except that the mixing ratio of LiNi1/3Co1/3Mn1/3O2 to LiMn2O4 was 30:70.
A battery was manufactured in the same manner as in Example 1, except that a mixture of LiNi1/3Co1/3Mn1/3O2 having an average particle diameter (with respect to capacity) of 0.12 μm/mAh and LiMn2O4 having an average particle diameter (with respect to capacity) of 0.23 μm/mAh was used as the cathode active material.
A battery was manufactured in the same manner as in Example 1, except that a mixture of LiNi1/3Co1/3Mn1/3O2 having a powder conductivity of 9×104 S/cm at a powder density of 2.75 g/cc and LiMn2O4 having a powder conductivity of 5×10−6 S/cm at a powder density of 2.80 g/cc was used as the cathode active material.
A battery was manufactured in the same manner as in Example 1, except that a mixture of carbon having a specific surface area (with respect to capacity) of 0.007 m2/mAh and carbon having a specific surface area (with respect to capacity) of 0.002 m2/mAh was used as the anode active material.
A battery was manufactured in the same manner as in Example 1, except that a mixture of carbon having a powder conductivity of 10 S/cm at a powder density of 1.1 g/cc and carbon having a powder conductivity of 25 S/cm at a powder density of 1.5 g/cc was used as the anode active material.
Energy per unit volume of each of the batteries manufactured according to Examples 1 to 6 and Comparative Examples 1 to 5 was measured and measurement results were compared. Charging and discharging were performed between 3.0 and 4.2 V, and charging was measured at a constant current and a constant voltage (CC/CV) and discharging was measured at CC. An energy of 3 C was confirmed under the condition that 1 C is 13 A in measuring C-rates of the batteries.
TABLE 1
Relative comparison
between energies
Vs. Example 1 (%)
Example 1
100
Example 2
104.2
Example 3
99.6
Example 4
102.3
Example 5
99.0
Example 6
101.2
Comparative Example 1
93.5
Comparative Example 2
92.2
Comparative Example 3
91.9
Comparative Example 4
88.3
Comparative Example 5
92.3
Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope and spirit of the invention as disclosed in the accompanying claims.
As described above, a lithium secondary battery according to the present invention uses, as an anode active material, amorphous carbon having a higher energy density (300 mAh/g or more) than conventional amorphous carbon and uses, as a cathode active material well balanced with the anode active material, a mixture of a layered-structure lithium transition metal oxide and a spinl-structure lithium manganese oxide in a predetermined ratio, whereby the lithium secondary battery achieves output characteristics well suited to electric vehicles, and the like and also exhibits enhanced energy density characteristics.
Lee, Jieun, Park, Su-min, Han, Chang Joo, Han, Kyunghee
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